1. Field of the Invention
The present invention relates to a clutch actuator for a differential assembly, and more particularly to a gear module for the clutch actuator in the differential assembly providing limited slip and locking capabilities.
2. Description of the Prior Art
Conventionally, differentials well known in the prior art, are arranged in a power transmission system of a motor vehicle to allow a pair of output shafts operatively coupled to an input shaft to rotate at different speeds, thereby allowing the wheel associated with each output shaft to maintain traction with the road while the vehicle is turning. Such a device essentially distributes the torque provided by the input shaft between the output shafts. However, these types of differentials known in the art as an open differentials, i.e. a differential without clutches or springs, are unsuitable in slippery conditions where one wheel experiences a much lower coefficient of friction than the other wheel; for instance, when one wheel of a vehicle is located on a patch of ice or mud and the other wheel is on dry pavement. In such a condition, the wheel experiencing the lower coefficient of friction loses traction and a small amount of torque to that wheel will cause a xe2x80x9cspin outxe2x80x9d of that wheel. Since the maximum amount of torque, which can be developed on the wheel with traction, is equal to torque on the wheel without traction, i.e. the slipping wheel, the engine is unable to develop any torque and the wheel with traction is unable to rotate. Thus, the necessity for a differential, which limits the differential rotation between the output shafts to provide traction on slippery surfaces, is well known.
A number of devices have been developed to limit wheel slippage under such conditions. Conventionally, they use a frictional clutch between the side gears and the differential casing. The frictional clutch may be selectively actuated by various hydraulic or electrical actuator assemblies, which may be external to the differential case or may be constructed of elements disposed inside the differential casing. Typically, those actuator assemblies are rather complex, expensive, laborious in assembly, and require extensive machining of a differential housing.
The present invention provides an improved electronically controlled differential assembly providing limited slip capabilities.
The differential assembly in accordance with the preferred embodiment of the present invention includes a rotatable differential case housing a differential gearing rotatably supported in the case and a pair of opposite side gears in meshing engagement with the differential gearing to permit differential rotation thereof. The differential assembly includes a friction disk clutch assembly disposed within the differential case and provided to lock the differential assembly. The friction clutch assembly includes a number of alternating outer friction plates non-rotatably coupled to the differential case and inner friction plates splined to a thrust collar disposed within the differential case coaxially to the side gears and adapted for loading the friction clutch plates when actuated. An electronic selectively controllable clutch actuator assembly is provided for axially displacing the thrust collar in order to load the friction assembly when needed, thus providing the differential assembly with a limited slip function. The clutch actuator assembly including an actuator motor, a clutch actuator, and a gear module for drivingly coupling the actuator motor to the clutch actuator. The gear module includes a casing having a first mounting flange for fixing the casing to a differential housing and a second mounting flange for fixing the casing to the actuator motor, two gear support arms outwardly extending from the first mounting flange into the differential housing through an opening therein, a gear shaft supported by the gear support arms, and a pair of coaxial reduction gear members drivingly coupled to the gear shaft. One of the reduction gear members is drivingly coupled to the actuator motor and the other of the reduction gear members is drivingly coupled with the clutch actuator.
Therefore, the differential assembly in accordance with the present invention is simple, compact, inexpensive in manufacturing, easy to assemble, and provides improved manufacturability and serviceability.